This invention relates to an exposure apparatus and, more particularly, to a pattern inspecting system or a substrate processing procedure monitoring system using such an inspection system. In another aspect, the invention is concerned with an exposure apparatus having an inspection system or a substrate processing procedure monitoring system such as above. The present invention is particularly suitable for determination of optimum exposure condition promptly or in real time to perform an exposure step in lithographic process, among manufacturing processes for production of devices such as semiconductor devices (e.g., IC or LSI), image pickup devices such as CCD, display devices such as liquid crystal panels, or magnetic heads, for example, on the basis of monitoring procedure in a processing system used in the lithographic process. The invention is applicable specifically for detection of any failure in a processing step promptly, to ensure process control.
Recently, the degree of integration of semiconductor device such as IC or LSI has been increased considerably, and fine processing technology of semiconductor wafer has also been much advanced. In this fine processing technology, many proposals have been made to a reduction projection exposure apparatus (stepper) wherein an image of a circuit pattern of a mask (reticle) is formed on a photosensitive substrate by a projection optical system (projection lens) and wherein the photosensitive substrate is exposed in step-and-repeat method.
In such steppers, a circuit pattern of a reticle is projected, in a reduced scale, at a predetermined position on the surface of a wafer through a projection optical system having a predetermined reduction magnification. After completion of one projection transfer operation, a stage on which the wafer is placed is moved by a predetermined amount. Then, the transfer operation is repeated. This procedure is repeated to perform exposure of the whole wafer surface.
Generally, in order to assure transfer of fine circuit pattern by use of a stepper having a projection optical system, it is important to set exposure condition such as wafer exposure amount or wafer focus position (wafer position with respect to a direction of an optical axis of the projection optical system) appropriately.
To this end, in conventional steppers, trial printing process (send-ahead) is performed prior to initiation of mass-production procedure. In such trial printing process, the exposure condition, that is, at least one of focus position and exposure amount (shutter time) is changed successively with respect to different shots. After printing of a photosensitive substrate, it is treated by a developing process, and the line width of a straight pattern developed is measured by use of an optical microscope or a line-width measuring device. Optimum exposure condition is then determined.
As regards lateral direction of wafer shot layout, for example, the exposure process may be performed with constant focus value while changing exposure amount (shutter time) successively by regular amount. As regards longitudinal direction of the wafer shot layout, the exposure process may be performed with constant exposure amount while changing focus value successively by regular amount.
Then, the line width of a resist pattern (LandS pattern) of lines and spaces in each shot, as defined through the developing process, may be measured by use of a scanning electron microscope (SEM). On the basis of this, optimum focal point position and optimum exposure amount may be determined.
In this procedure, however, measurement of the line width of a resist pattern on a wafer through a scanning electron microscope, for example, for setting optimum exposure condition (exposure amount or focus position) in steppers requires a long processing time.
Further, an exposure wafer has to be processed by a developing step, an etching step and an ashing step, for example. Through these steps, a final pattern is formed on the wafer. Thus, depending on a condition in such processing step after exposure, there is a possibility that the state of formation of such final pattern on the wafer varies.
In mass-production of devices, the state of formation of such pattern should desirably be constant. However, due to various factors, the condition in a processing step may change which in turn may cause a decrease in yield. It is therefore necessary to monitor the processing step periodically and to control the same.
Usually, such process control is based on measurement of a line width of a straight pattern by use of an optical microscope or a line-width measuring device. Thus, it takes a long time for the process control.
It is an object of the present invention to provide a pattern inspection system by which optimum exposure condition can be determined in a short time period.
It is another object of the present invention to provide a projection exposure apparatus having such a pattern inspection system.
In a pattern inspection system of the present invention, the state of sensitization of a resist sensitized by exposure (i.e. latent image) or the state of formation of a sensitized pattern such as a line-and-space pattern after being developed, is measured on the basis of a change in light projected under different light incidence conditions, for example, a change in intensity of reflection light or a change in state of polarization. An optimum exposure condition is determined on the basis of a measured value. Mass-production exposure of wafers is performed under that optimum exposure condition.
It is a further object of the present invention to provide a substrate processing step monitoring system by which quick and assured process control is enabled and production of large-integration pattern is enabled. In a substrate processing step monitoring system of the present invention, for control of a developing step, for example, the state of sensitization of an exposed resist (i.e. latent image) before developing process and the state of formation of a sensitized pattern such as a line-and-space pattern after the developing process, are measured on the basis of a change in projected light, for example, a change in intensity of reflection light or a change in state of polarization. Then, on the basis of comparison of measured values, a change in state of pattern formation is detected and whether the fault has been created during the developing process or before the developing process is discriminated.
In accordance with a further aspect of the present invention, there is provided a pattern inspection system for detecting a state of a pattern formed on an object, said system comprising: light projecting means for projecting input light on to a sensitized pattern defined on the object; light receiving means for receiving signal light from the sensitized pattern; processing means for detecting a change in the light by use of a signal from said light receiving means to detect the state of formation of the sensitized pattern; and control means for changing a light incidence condition of light from said light projecting means.
In accordance with a still further aspect of the present invention, there is provided a projection exposure apparatus for projecting a pattern of a first object, as illuminated with exposure light, on to a second object coated with a photosensitive material through a projection optical system to thereby form a sensitized pattern on the second object, said apparatus comprising: light projecting means for projecting input light on to the sensitized pattern with different conditions of light incidence; light receiving means for receiving signal light from the sensitized pattern; and processing means for detecting a change in the input light by use of a signal from said light receiving means to detect the state of formation of the sensitized pattern.
In accordance with a yet further aspect of the present invention, there is provided a projection exposure method for projecting for projecting a pattern of a first object on to a second object coated with a photosensitive material through a projection optical system, said method comprising the steps of: illuminating the pattern of the first object with exposure light while changing an exposure condition and projecting the pattern of the first object so illuminated on to the second object, whereby a plurality of sensitized patterns are formed on the second object; projecting input light from light projecting means to the sensitized patterns under different conditions of light incidence; receiving, through light receiving means, signal light from the sensitized patterns; detecting a change in input light by use of a signal from the light receiving means to detect a state of formation of the sensitized patterns through processing means; and controlling exposure condition of the second object through control means, on the basis of a signal from the processing means.
In accordance with a further aspect of the present invention, there is provided a substrate processing procedure monitoring system, comprising: light projecting means for projecting input light on to a pattern defined on a substrate; light receiving means for receiving signal light from the pattern; detecting means for detecting a change in input light by use of a signal from said light receiving means; and processing means having inspecting means for detecting a state of formation of the pattern on the basis of detection by said detecting means, for memorizing and comparing results of detection of the state of formation of the pattern before and after the processing procedure to the substrate.
In accordance with a still further aspect of the present invention, there is provided a substrate processing procedure monitoring method, comprising the steps of: projecting input light on to a periodic pattern defined on a substrate; receiving, through light receiving means, signal light from the pattern; detecting a change in input light by use of a signal from the light receiving means; detecting a state of formation of the pattern on the basis of detection at said detecting step; and memorizing and comparing results of detection of the state of formation of the pattern before and after the processing procedure to the substrate.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.